I had a dodgy speedo, kept switching on and off, so changed the sensor behind the engine and it was fine, how ever after booting it the other day it's died again. I put the old one back in but that gave me no life so now I'm lost!! But I'd say first port of call new sensor. Also might be worth taking off the engine cover when changing them, because once I got my arm down there it scraped the hell out of it pulling it back up !!